Load indicating fastener systems method and apparatus

ABSTRACT

A fastener system employs a portable, sensing device, such as one or more reactance capacitors or an image processor such as a camera or a laser, which removably attaches adjacent to the fastener to detect and measure the change in a gap or specialized form of the bolt head or associated washer caused by the relative movement of portions of the fastener system when the fastener is under strain without contacting the sensed portions undergoing the significant relative movement. Associated electronic components process and indicate the clamp load of the fastener system. Embodiments of the relatively moving portions which provide a resilient, repeatable changing gap or form under load include inward movement of a cylindrical bar anchored in a bore in the head and shank relative to the flush outer top surface of the bolt head, a washer form change relative to the outer surface of the clamped joint, a form change in one portion of a bolt head relative to another portion of the bolt head, and a washer form change relative to a bolt head form change.

BACKGROUND OF THE INVENTION AND PRIOR ART

1. Field of the Invention

This invention relates to load indicating fastener systems that areadapted to indicate loads to which they are subjected and, morespecifically, to a non-contact electronic device, such as a reactancecapacitor, which measures a changing air gap or form produced when afastening system is strained, and, more specifically, to a non-contactimage processing or laser device, which measures a changing air gap orform produced when a fastening system is strained.

2. Description of the Related Art

It is desirable that applied fasteners systems should be accuratelytightened to the designed load levels in order to ensure the structuralintegrity of the bolted joint. It is well known that indicating straingives a true representation of the load induced in the fastener systems.Torque wrenches are commonly used for tightening fasteners topredetermined torque levels, but they are subject to unpredictablefriction so that the strain produced can be widely inaccurate. In otherwords, controlling torque will not lead to accurate loading of afastener system.

Prior Contact-Type Fastener Extension Measuring Devices

Some measuring devices, for instance linear transducers, need to makephysical contact to be functional. These contact methods are inherentlydifficult to use in the field. The measurements of strain are extremelysmall and any surface contamination (corrosion, dirt, natural abrasives,in service damage, etc.) leads to significant errors. Accordingly, it isan object of the present invention to measure strain by using anon-contact device and method.

Prior Non-Contact-Type Fastener Extension Measuring Devices And Methods

Previous non-contact-type devices and methods of measuring the extensionof a fastener under strain have utilized electrical components withineach individual fastener, typically a bolt or a stud. These earliermethods have a number of significant problems associated with them.

One problem with previous non-contacting measuring devices is that it isprohibitively expensive to instrument each individual fastener withelectrical components. Additionally, the integrated instrumentationcompromises the integrity of the fastener and is not suitable for therugged environments of many applications. Accordingly It is an object ofthe present invention is to provide a cost effective load indicatingfastener in which the fastener itself carries no electric parts.

A further problem with previous non-contacting measuring devices is thatthey typically require complex modification of the fastener making themanufacturing process difficult. Accordingly, it is an object of thepresent invention to measure the fastener extension using a simpledevice and method which require only a slight modification to thefastener system which is readily and easily incorporated during themanufacturing process.

BRIEF SUMMARY OF THE INVENTION

Set forth below is a brief summary of the invention which achieves theforegoing and other objects and provides the foregoing and hereafterstated benefits and advantages in accordance with the structure,function and results of the present invention as embodied and broadlydescribed herein. Applicant's invention includes independently both theapparatus and the methods described herein which achieve the objects andbenefits of the present invention. Both formats of the invention aredescribed below, and it is applicants intention to claim both formatseven though from time to time below for purposes of clarity and brevityapplicant will use either one or the other format to describe variousaspects and features of the invention.

According to the present invention a load indicating fastener system isprovided which comprises a body to which strain is applied when thefastener is in use, a load sensing means having parts arranged forrelative movement in response to change in length or form of the body oran associated washer design under an applied strain, and a separatenon-contact gap measuring device, such as an electronic device includinga reactance capacitor, or such as an image processing device, or such asa laser device, (hereinafter collectively and/or separately referred toas “a non-contact gap measuring device”) which, when secured adjacent tothe fastener, registers the said relative movement of the moving partsby a non-contact method.

The fastener system may be in the form of a bolt or stud, a nut andwashers, or it may take other forms. In the form of a bolt, the body ofthe fastener comprises a head and shank which may be of substantiallystandard form. Similarly, in the form of a stud, the body comprises ashank which may be of substantially standard form. In either of saidforms, a washer may incorporate the means of indicating the moving partsbeing sensed by a separate non-contact gap measuring device of the typedescribed above. In the case of bolt or stud, the load-sensing elementresponds to a change in length of the shank under the applied strain. Inthe case of the washer, the load sensing element senses the change ofshape in the form of the washer under applied strain. Conveniently, thegap measuring device can be secured at the bolt head, thread end, studend, or washer where it can easily be secured when the fastener systemis in use.

The load-sensing element indicates changes in the length of the body ofthe fastener, or changes in the form of the washer, or changes in theform of the bolt head as the fastener system is being secured and whenthe fastener system has been secured. Thus, as the fastener system isbeing secured, the applied loads will be registered by the non-contactgap measuring device which will indicate when the fastener systemreaches a required working load. The non-contact gap measuring devicecan be attached to the fastener system and obtain a measurement whichcan be displayed on a computer monitor 24 or other display unit. Thismeasurement can be used during the tightening process. The measurementcan be used after the initial tightening to inspect for any changes inthe initial strain condition.

Actual fastener system loads may be indicated on the monitor 24 and anelectrical output can be used to control power tightening tools (notshown) or indicate a warning when the fastener system desired load hasbeen achieved.

The load sensing means may be arranged to register applied loads up tothe fastener system material proof loads, (proof load is the maximumload that can be sustained before there is a permanent change from itsoriginal dimensions.)

The creation of a gap that changes with changing strain can be achievedin various ways. In the preferred embodiment the means to create thischanging gap comprise a load-sensing element disposed in the directionin which strain is applied to the body when the fastener system is inuse, and has an anchorage part. The anchorage part is rigidly anchoredto the body at a part of the body in which there is movement when thefastener is applied for use. An air gap between the non-contact gapmeasuring device and the element widens or reduces depending on whetherthe fastener is being secured or looses strain. The non-contact gapmeasuring device reacts by measuring the air gap and registers theapplied load on a monitor 24. Preferably the load-sensing element ismade of the same material, or at least has the same coefficient ofthermal expansion, as the material of the body. This way, changingtemperatures at which the fastener system may be used will not affectthe functioning of the load-sensing element.

In a preferred embodiment the load-sensing element is a solid diameterbar, one end providing the anchorage part, the other free end to moverelative to the fastener. At least part of the load sensing element maybe located in a blind bore or passage in the body. When the load sensingmeans comprises an element, as described above, it may be provided by aninsert fitted into the blind end portion of the bore or passage. Theanchorage may be anchored into the base of the bore or passage. The boreor passage may have a smaller base portion in which the anchorage partis anchored. Conveniently the non-contact gap measuring device islocated at or near the free end of such a bore or passage. There may bedirect anchorage of the element to the body, for example by welding,threading or adhesive bonding, or the element may be anchored to thebase, which is suitably fixed to the body. The base of the bore orpassage may be in the form of a close interference bore into which theelement is pressed to provide a secure anchorage.

The load-sensing element may be arranged to operate over a given rangeof changes of length of the body under applied strain. This will usuallybe by elongation of the body from the unloaded condition up to thematerial proof load. When the load is applied to strain the body, theload sensing element moves into the body away from the zero datum (datummeans the fixed part on the fastener upper head face that does notmove). The non-contact gap measuring device attaches to the body andmeasures the difference between the datum point (reference point orform) on the body and the load sensing element, and the non-contact gapmeasuring device is calibrated to indicate load.

For a given elongation under the proof load a required original lengthcan be calculated from:$\frac{{Original}\quad {length}\quad E \times A \times {extension}}{load}$$\begin{matrix}{{Where}\text{:}} & \quad \\\quad & {E = {{Youngs}\quad {Modulus}\quad {for}\quad {the}\quad {material}\quad {of}\quad {the}\quad {{body}.}}} \\\quad & {A = {{Cross}\quad {section}\quad {area}\quad {of}\quad {the}\quad {{body}.}}}\end{matrix}$

For different cross sectional areas and/or proof loads the requiredoriginal length will vary. For a range of fastener sizes, proof loadsensing elements of different lengths may be provided, as required.However, it is generally easier and more economical for production toprovide load sensing element means for the fasteners in accordance withthe invention with load sensing elements of a standard length and tocompensate for the differences by the non-contact gap measuring device.

It is possible for the present invention to give a highly accurateindication of the fastener system applied loads. The indication from thenon-contact gap measuring device of the applied loads enables a personto see readily what the applied loading on the fastener system is. Thiscan be from a portable battery operated monitor/display, which may behand held and connected to the non-contact gap measuring unit by anumbilical connector.

The fastener system may be manufactured without being substantially moreexpensive than a conventional fastener or similar type. For example, thebores may be pierced during originally manufacturing process. Furthermore, a conventional fastener may be readily adapted to include the loadsensing means in accordance with the present invention.

In another form, the load sensing may be arranged to register appliedloads up to the proof load for the material by a load-indicating washer.The washer is designed to deflect under the fastener system strain andthe non-contact gap measuring device measures the deflection against astatic part of the washer/bolt. The non-contact gap measuring devicesare calibrated to indicate the fastener system load as explained above.

In another form, the load sensing may be arranged to register appliedloads up to the proof load of the material by measuring the deflectionof a specially designed bolt head when the bolt is under strain, themeasurement being taken from two parts which are moving relative to eachother when the bolt is under strain. The non-contact gap measuringdevice is calibrated to indicate the fastener system load as explainedabove.

The method used in the preferred embodiment of the present invention ismeasurement by reactance which is:${{Capacitive}\quad {reactance}} = \frac{1}{2\pi \quad {FC}}$${{and}\quad {capacitance}} = \frac{D \times A}{G}$${{Hence}\quad {reactance}} = \frac{G}{2\pi \quad {FDA}}$Displacement = change  in  gap $\begin{matrix}{Where} & {F = {{Frequency}\quad ({hertz})}} \\\quad & {C = {{capacitance}\quad ({farads})}} \\\quad & {D = {{dielectric}\quad {constant}\quad \left( {{air} = 1} \right)}} \\\quad & {A = {{area}\quad \left( {{inch}\quad {squared}} \right)}} \\\quad & {G = {{gap}\quad ({inch})}}\end{matrix}$

Set forth below are some of the advantages of the present invention:

1. A non-contact gap measuring device comprising all of the necessaryelectronics measures a changing air gap or form produced when afastening system is strained without physically coming into contact withthe moving parts being measured.

2. Measuring by non-contact minimizes error from contamination or theenvironment.

3. The distance being measured is determined from the average mean valueof the entire surface being measured, which is not the case for contactmethods.

4. The device and method are cost effective because the cost of thefastener will not change significantly, if at all, since only slightmodifications need to be made to the fastener to implement theinvention.

5. The fastener carries no electric parts.

6. The design modifications to the fastener system will be incorporatedduring its manufacturing process.

7. The fastener system is suited for even the most rugged applications.

8. Displacement is directly proportional to reactance and will give alinear graph.

9. The fastener system load indication is highly accurate andrepeatable.

10. The system is portable and can be used in the field to readily checkand easily read the applied loads.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a partly sectioned elevational view of the present inventionshowing the modifications to a fastener and the measuring elementembodied into it for measuring the gap Also shown is the portablereactance capacitor head with a ring type reactance capacitor and acylindrical type reactance capacitor. The ring type reactance capacitormeasures the gap between the face of the ring type reactance capacitorand the fixed part of the fastener. The cylindrical type reactancecapacitor measures the gap between the face of cylindrical typereactance and the upper free end of the measuring element. Thenon-contact gap measuring device computes the difference between thefree end of the measuring element and the datum plane (reference). Thenon-contact gap measuring device computes the difference between the twomeasurements, and the result is accurately calibrated to indicateclamping load generated by the fastener when it is in use.

FIG. 2 is a view similar to FIG. 1 showing the fastener described inFIG. 1 without the portable head.

FIG. 3 is a view similar to FIG. 1 showing an alternative option formeasuring the gap by using only a cylindrical type reactance capacitor.The portable head is secured to the fixed part of the fastener datumface. The cylindrical type reactance capacitor measures the gap betweenthe face of th cylindrical type reactance and the upper free end of thesurface of the measuring element. The non-contact gap measuring devicecomputes the different measurement of the gap and is calibrated toindicate clamping load induced by the fastener when it is in use.

FIG. 4 is a view similar to FIG. 1 showing a specially designed washerthat deflects when the fastener system is under strain and annon-contact gap measuring device for measuring the gap. The reactancecapacitor non-contact gap measuring device, when secured to the boltedjoint, measures the gap between the face of the reactance capacitor andthe part being measured on the washer.

FIG. 5 is a view similar to FIG. 1 showing a specially designed washerthat deforms the head of the fastener so that two different parts of thehead can be measured relative to each other by the reactance capacitornon-contact gap measuring device when the fastener is under strain.

FIG. 6 is a view similar to FIG. 1 showing a further modified form ofthe present invention with an image processing or laser type gapmeasuring device fitted for use.

FIG. 7 is a view similar to FIG. 1 showing a fastener head which ismodified to deflect under load when the fastener is subject ed to atensile force.

FIG. 8 is a view similar to FIG. 1 showing a further modification of thepresent invention having a specially designed washer that deflects andalso deflects the fastener head under load when the fastener issubjected to a tensile force.

FIG. 9 is a view similar to FIG. 1 showing a further modification of thepresent invention in which the specially designed washer of FIG. 9deflects under load when the fastener is subjected t o a tensile forceand the change in the gap is measured from the side of the system.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in detail, as in FIGS. 1, 2, there isshown an embodiment of a load indicating faster in bolted joint 25 inwhich in order to measure the changing gap between the faces of thereactance capacitors 15, 16 and shank 4, there is provided a boltfastener system 1 having a metal body 2 made from steel, for example,which includes a hexagon head 3 and a shank 4, the shank 4 having anexternally screw-threaded portion 5 spaced from the head 3 by a plaincylindrical portion 6, washers 26, 27, a nut 28, and a reactancecapacitor 15A which, in the FIG. 1 embodiment, includes the cylindricalreactance capacitor 15 and the ring reactance capacitor 16 for measuringthe changing gap.

Drilled into the body 2, co-axially with its rotational axis, is a blindbore 7 which extends from the top of the head 3, through the head 3 andinto the shank 4 for is approximately a quarter the length of the plaincylindrical portion 6. The closed inner end of the bore 7 is a losetolerance smaller counterbore 9, which serves as an anchor for measuringelement 8. Supported in the bore 7 is a load sensing means, whichcomprises the measuring element 8, made from the same material as thebody 2. The element 8 is anchored in the bore 7 at counterbore 9. Theanchorage could, for example, be pressed into bore 9 or may be securedtherein by any of various types of fixing.

The upper surface of head 3 is machined to form a location spigot 10,upper datum face 11 and a lower face 12. The element 8 free end 8A isground flush with the head 3 upper datum face 11. The element 8 respondsto loads applied to the shank 4 by nut 28 when the fastener is in use.The response is related to the extension of the shank 4 under appliedloads. It is appropriate for the element 8 to sense applied loads and toindicate said loads up to the proof load for the material of the body 2.Therefore, the element 8 is arranged to respond to the extension of theshank 4 up to the extension caused by the proof load. For this to beachieved the element 8 is set in bore 7 of the body such that theanchorage in counterbore 9 moves the element 8 into or out of the body 2depending on the load being induced into the shank 4. Therefore, theelement 8 free end a moves relative to the head 3 upper datum surface 11depending upon whether the shank 4 is being loaded or unloaded. When theshank 4 is free from load, the element 8 and the head upper datumsurface 11 are flush which indicates no load in the shank 4. Because theshank 4 material obeys Hookes Law, the gap created between the element 8free end 8A and the head 3 upper datum surface 11 can be calibrated toindicate load by the portable head measuring device 13 up to the proofload of the shank 4 materials. Provided the proof load is no t exceeded,the load indication will be always repeatable.

The portable head 13 carries the reactance capacitors 15, 16 and isconstructed to accurately locate on to the head 3 locating spigot 10.The portable head 13 is secured to the head 3 by a magnet 14 mounted anthe bottom of portable head 13, or portable head 13 may be secured tohead 3 by other known means. The ring type reactance capacitor 16measures the gap between the face 11B of the capacitor 16 and the head 3upper datum surface 11. The cylindrical type reactance capacitor 15measures the gap between the surface 11A of the capacitors 15 and thefree end 8A of element 8. The said gaps between the said surfaces andthe two capacitors 15, 16 are compared by the non-contact gap measuringdevice and associated electronics which include reactance capacitors 15,16, capacitance amplifier 22, signal conditioner 23, and display 24 andwhich are calibrated to indicate load that the shank 4 is subjected toduring its use.

The ring type reactance capacitor 16 of FIG. 1 is replaced in FIG. 3 bya solid metal disc 17 which is mounted in portable head 17A and whichabuts the head 3 upper datum face 11. The reactance capacitor 15 stilloperates in the same way as described for FIG. 1. All other details areas described for FIG. 1. The reactance capacitor 15 compares thedifference between the datum surface 11 and the movement of element 8when the system is in use.

As shown in FIG. 4, the fastener system 1 deflects washer 18 when it isin use. The reactance capacitor 31 measures the gap between the face 32of the capacitor 31 and the washer 18 surface 20. The system operates asdescribed for FIG. 1.

Shown in FIG. 5 is specially designed washer 21 which deflects the head3 of the bolt and the ring reactance capacitors 16A, 16B, mounted inportable head 33A and located atop the bolt head 3 by location peg 33,compare two parts of the head 3 relative to each other to indicate load.Otherwise the system is as described for FIG. 1.

As seen in FIG. 6, the portable head 34A carries the camera or laser 34which is connected to image processor 35 which is connected to readout36. Portable head 34A is constructed to accurately locate onto the head3 locating spigot 10. The portable head 34A is secured to the head 3 bya magnet 14 mounted on the bottom of portable head 34A, or portable head34A may be secured to head 3 by other known means. The camera or lasersystem 34, 35 measures the gap between the free end face 8A of theelement 8 and the upper datum surface 11 of head 3. The gaps between thedatum surface 11 and the free end 8A of the element 8 are compared bythe camera or laser system 34, 35 and calibrated to indicate load thatthe shank 4 is subjected to during its use. The camera 34 can bereplaced by a laser 34 and coupled to a processor 35 and to a readout 36or to a computer (not shown).

As seen in FIG. 7 an alternative option for measuring the fastener head40 deflection when the system is under load. The specially designed head40 is shaped with an annular groove 41, a spigot 10 having an annularouter face 42 surrounding a recess 43 having a floor 44 and cylindricalwall 45, and the portable monitor 34A with the camera or laser 34detects the change in shape of the head when under load. The electronicsis calibrated to recognize the load scale from zero to proof load of thematerial and indicates load induced into the fastener.

FIG. 8 is the same as that described in FIG. 7, but a special washer 21causes the specially designed head 46, having recess 43 with floor 44and wall 45 and outboard concave face 47, to deflect.

FIG. 9 is the same as that described in FIG. 8, but the changing shapeof the special washer 22, due to the fastener system loading up to thematerial's proof load, is detected by either the camera or laser 34 asshown.

The foregoing description of preferred embodiment and best mode of theinvention known to applicant at the time of filing the application hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed, and obviously many modifications and variations arepossible in the light of the above teaching. The embodiment was chosenand described in order to best explain the principles of the inventionand its practical application to thereby enable others skilled in theart to best utilize the invention in various embodiments and withvarious modifications as are suited to the particular use contemplated.It is intended that the scope of the invention be defined by the claimsappended hereto.

What is claimed is:
 1. A load measuring apparatus comprising: anexternally mounted camera or laser supported in a portable sensing headand configured and constructed for sensing a changing gap, between, onthe one hand, an end face of a bar in and anchored to a base of a borein a bolt head and shank of a fastener system and, on the other hand, adatum face of the bolt head of the fastener system, caused bylongitudinal extension of the shank under strain relative to the datumface on the bolt head without contacting the relatively moving portionsof the fastener system, and a generating circuit responsive to thesensed changing gap for providing an output signal indicative of a clampload applied to the fastener system.
 2. A load measuring apparatuscomprising: a camera or laser, externally removably positionable andsupportable on a portable detector head atop a fastener system to bevisually or light beam coupled, respectively, to a bolt head of thefastener system along an axis parallel to the longitudinal axis of thefastener system configured and constructed for sensing a changing formcaused by a deflection of a first portion of the bolt head relative to asecond portion of the bolt head when the fastener is under strainwithout contacting the sensed portions of the bolt head, and agenerating circuit responsive to the sensed changing form for providingan output signal indicative of a clamp load applied to the fastener. 3.The apparatus of claim 2 further comprising: a bolt head shape includinga central recess in an outboard face.
 4. The apparatus of claim 2further comprising: a bolt head shape including a concave outboard face.5. The apparatus of claim 2 further comprising: a bolt head shapeincluding an inboard annular groove in the underside of the bolt headand a spigot on the top side of the bolt head with a central recsstherein.
 6. The device of claim 2 further comprising the changing formis a bolt head and a washer combination of the fastener system understrain.
 7. A measuring device comprising a portable sensing head, havinga first cylindrical capacitor plate fixedly supported in the portablesensing head, eternally removably positionable atop an integral headportion of a fastener system, and constructed and configured fordirectly capacitively coupling to a second cylindrical capacitor platemovably supported in the fastener system to form a capacitor for use ina circuit for detecting a changing gap, measured from a reference datumplane of the bolt head of the fastener system, the changing gap beingproduced in the fastener when the fastener system is under strain andcausing a variance in the capacitive reactance of the detection circuitwithout the portable sensing head contacting the second movablecapacitor plate.
 8. The apparatus of claim 7 further comprising: a bolthead shape including a central recess in an outboard face.
 9. Theapparatus of claim 7 further comprising: a bolt head shape including aconcave outboard face.
 10. The apparatus of claim 7 further comprising:a bolt head shape including an inboard annular groove in the undersideof the bolt head and a spigot on the top side of the bolt head with acentral recss therein.
 11. The device of claim 7 further comprising thechanging form is a bolt head and a washer combination of the fastenersystem under strain.
 12. A measuring device comprising a sensing circuithaving a first capacitor plate externally removably positionable besidea deflectable washer mounted between an integral head portion of afastener system and a workpiece, and constructed and configured fordirectly capacitively coupling to a second capacitor plate movablysupported on the washer of the fastener system to form a capacitor foruse in a circuit for detecting a changing gap between the first andsecond capacitor plates, the changing gap being produced when thefastener system is under strain and causing a variance in the capacitivereactance of the detection circuit without the sensing circuitcontacting the second movable capacitor plate.
 13. A measuring devicecomprising a portable sensing head, having multiple first capacitorplates fixedly supported in the portable sensing head, externallyremovably positionable atop an integral head portion of a fastenersystem, and constructed and configured for directly capacitivelycoupling each of the first capacitor plates to a common second capacitorplate movably supported on the fastener system to form multiplecapacitors for use in a circuit for detecting a changing form of thebolt head of the fastener system, the changing form being produced inthe fastener when the fastener system is under strain and causing avariance in the capacitive reactance of the detection circuit.
 14. Ameasuring device comprising a portable sensing head, having first,spaced apart, capacitor plates fixedly supported in the portable sensinghead, externally removably positionable atop an integral head portion ofa fastener system, and constructed and configured for directlycapacitively coupling the first capacitor plates to a second capacitorplate a portion of which is movably supported in the fastener system toform multiple capacitors for use in a circuit for detecting a changinggap, measured from a reference datum plane of the bolt head of thefastener system, the changing gap being produced in the fastener whenthe fastener system is under strain and causing a variance in thecapacitive reactance of the detection circuit without the portablesensing head contacting the second movable capacitor plate.
 15. Ameasuring device comprising a portable camera or laser which, whenexternally removably positioned and supported alongside of a bolt headand deflectable washer of a fastener system and visually or light beamcoupled, respectively, to the bolt head and washer along an axis cuttingthe longitudinal axis of the fastener system at a substantial angle,detects a changing gap or form produced in the fastener when the systemis under strain without contacting the sensed portions of the fastenerundergoing significant relative movement.
 16. A device of any one ofclaims 1-15 used to indicate load of the fastener.
 17. A device of anyone of claims 1-15 used to indicate when the load on the fastenerreaches a predetermined load.
 18. A device of any one of claims 1-15used to communicate with a fastener tightening mechanism.
 19. A deviceof any one of claims 1-15 used to transmit a signal for remote sensing.20. A device of any one of claims 1-15 used to determine that thefastener system is still within the desired design pre-load window. 21.A device of any one of claims 1-15 used to indicate load at elevatedtemperatures.
 22. A device of any one of claims 1-15 used to give awarning or signal when a desired fastener system pre-load is reached.23. The device of any one of claims 1-11, 13-14 further comprising: anattachment portion having an end portion for mounting the detector headatop a head of the fastener.
 24. The device of claim 23 wherein the endportion further comprises: a recessed opening In the detector head alongits longitudinal axis terminating in a flat end face orthogonal theretofor fitting around a spigot of the fastener.
 25. The device of claim 23wherein the end portion further comprises: a recessed opening in thedetector head along its longitudinal axis for receiving a locator pegpositionable within the portable head and the fastener head for guidingthe detector head into a position relative to the fastener.
 26. Thedevice of claim 23 wherein the end portion further comprises: a magnetmounted therein.
 27. The device of claim 23 wherein the end portionfurther comprises: a friction fit with the spigot.
 28. The apparatus ofclaim 13 wherein the at least one reactance capacitor further comprises:a pair of concentrically mounted ring capacitors.
 29. The apparatus ofclaim 28 wherein the pair of ring capacitors further comprises: a bottomface of each capacitor is equally spaced from an end plane of thedetector head orthogonal to the longitudinal axis of the detector head.30. The apparatus of claim 14 wherein the multiple first capacitorplates further comprise: a cylindrically shaped capacitor mountedconcentrically with a ring shaped capacitor.
 31. The apparatus of claim30 wherein the cylindrically shaped capacitor mounted concentricallywith the ring shaped capacitor further comprises: a bottom face of eachcapacitor is equally spaced from an end plane of the detector headorthogonal to the longitudinal axis of the detector head.
 32. Theapparatus of claim 30 wherein the cylindrically shaped capacitor mountedconcentrically with the ring shaped capacitor further comprises: abottom face of each capacitor is spaced apart from each other and froman end plane of the detector head orthogonal to the longitudinal axis ofthe detector head.